The invention relates to an apparatus and a method of controlling the road speed of a motor vehicle.
In modern motor vehicles the road speed is usually controlled by means of a pedal, also known as an accelerator pedal, which is biased counter to its actuating direction into an inoperative position and through the actuation of which the drive torque and/or the drive power of the motor vehicle engine may be increased. When the driver of the motor vehicle wishes to lower the road speed, he reduces the actuating force exerted on the accelerator pedal in order to move the accelerator pedal back towards, or fully into, its inoperative position. If this is not sufficient to achieve the desired lowering of the road speed, the driver actuates a brake pedal, which is usually likewise provided in the motor vehicle.
From DE-A-24 20 252 an accelerator pedal arrangement for motor vehicles is known, which in the unloaded state of the accelerator pedal activates a parking brake. Upon actuation of the accelerator pedal the parking brake is released.
The object of the invention is to indicate an apparatus and a method, which simplify control of the road speed of a motor vehicle.
Proceeding from the initially described apparatus comprising a braking-force generator for controlling the road speed of a motor vehicle, said object is achieved according to the invention in that the braking-force generator builds up the predetermined braking force in a controlled manner when the accelerator pedal reaches its inoperative position and/or reduces the built-up braking force in a controlled manner when the accelerator pedal leaves its inoperative position. The predetermined braking force is therefore not made available abruptly but brought up e.g. according to a preselected ramp function. In an analogous manner, the built-up braking force is preferably reduced in a controlled manner when the accelerator pedal leaves its inoperative position.
According to an alternative of the apparatus according to the invention the device for detecting the inoperative position of the accelerator pedal, upon a movement of the accelerator pedal from the inoperative position into the neutral position, causes the braking-force generator to reduce the predetermined braking force in accordance with the accelerator pedal movement and vice versa. In said manner, a driver may himself purposefully proportion the braking function of the apparatus according to the invention within the preselected limits, i.e. up to the predetermined braking force, by moving the accelerator pedal to a greater or lesser extent and/or more or less quickly between the inoperative position and the neutral position. Given such a form of construction, the device for detecting the inoperative position of the accelerator pedal takes the form of a displacement sensor, e.g. a displacement potentiometer.
According to a simple form of construction of the invention, the device for detecting the inoperative position of the accelerator pedal may be e.g. a switch, which in the inoperative position of the accelerator pedal is actuated by the latter and supplies the braking-force generator with a signal, in response to which the braking-force generator generates the predetermined braking force. The accelerator pedal is movable from its inoperative position into a neutral position, from which a further movement of the accelerator pedal counter to the spring bias, i.e. in actuating direction, leads to an increase of the drive torque and/or drive power of the motor vehicle engine.
Thus, according to the invention the acceleration function conventionally associated with the accelerator pedal is supplemented by an active braking function, wherein said two functions are separated from one another by the neutral position of the accelerator pedal. For specific applications it may however also be advantageous additionally to allow the said braking function to operate in actuating direction of the accelerator pedal slightly beyond the neutral position, e.g. for reliably preventing the vehicle from rolling backwards on a hill.
The apparatus according to the invention leads to considerably simplified vehicle control. For example, in stop-and-go traffic, instead of constantly having to transfer the right foot back and forth between accelerator pedal and brake pedal, the accelerator pedal now merely has to be eased back into the inoperative position. During downhill travel, when the engine braking action is frequently insufficient to achieve adequate deceleration of the vehicle, by simply easing back the accelerator pedal the brake system may be actuated with the predetermined braking force. Equally, for stopping on ascending gradients, according to the invention an easing of the accelerator pedal back into its inoperative position will in most cases be sufficient to prevent the vehicle from rolling backwards. A subsequent starting operation is also made more comfortable because, to release the brake and increase the engine drive torque, the accelerator pedal may be moved from the inoperative position quickly into the neutral position and beyond, without the usual practice of first having to transfer the right foot (from the brake pedal to the accelerator pedal), with the result that there is now virtually no opportunity for the vehicle to roll back. The apparatus according to the invention offers advantages also during emergency braking operations because the braking operation is already initiated by easing back the accelerator pedal and so is initiated more quickly than was previously usual. According to the invention the predetermined braking force is normally lower, in most cases even markedly lower, than the maximum possible braking force.
As already mentioned, the apparatus according to the invention is preferably designed in such a way that the braking-force generator in the neutral position of the accelerator makes no braking force or, at any rate, substantially no more braking force available.
In preferred embodiments of the apparatus according to the invention, the dimension of the predetermined braking force is varied in dependence upon specific parameters. For example, in one embodiment the predetermined braking force is increased as the road speed rises, and vice versa. In said manner, by means of the accelerator pedal an effective braking function is maintained also at higher road speeds.
In another embodiment, the magnitude of the predetermined braking force is varied in dependence upon the way in which the motor vehicle is moved. For example, for a sporty driving style the predetermined braking force is set higher than for a steady and economical driving style.
In yet another embodiment, the predetermined braking force is varied in dependence upon the speed at which the accelerator pedal is eased back. For a rapid release of the accelerator pedal the predetermined braking force is in said case set higher than for an only gradual easing back of the accelerator pedal. In said manner, the stopping distance of the vehicle in emergency braking situations may be markedly shortened.
In a further embodiment, the predetermined braking force is varied in dependence upon the inclination of the road on which the vehicle is situated. By inclination, here, is meant a descending or ascending gradient. The greater the ascending or descending gradient, the higher the predetermined braking force is set.
The described dependencies of the predetermined braking force may advantageously also be combined.
According to the invention, the braking-force generator may be a driver-independently actuable vacuum brake booster, a hydraulically or pneumatically actuable brake booster, a pressure accumulator or a pump, in particular the pump of a brake slip control system, which nowadays is already standard equipment in many motor vehicles. The braking-force generator may however also be an electrically operated actuator of a vehicle brake itself.
To help the driver of a motor vehicle to become accustomed to the apparatus according to the invention, the latter is preferably designed in such a way that the dimension of the spring bias of the accelerator pedal counter to actuating direction increases when, from the inoperative position of the accelerator pedal, the neutral position is reached. In said manner the driver receives clear feedback about the attainment of the neutral position because, from the neutral position on, the resistance which the driver has to overcome for further actuation of the accelerator pedal increases.
The previously described behaviour of the apparatus according to the invention may be achieved, for example, by a displacement potentiometer, which cooperates with the accelerator pedal and comprises a fettered spring acting in actuating direction of the accelerator pedal. The fettering is in said case such that the spring force acting in actuating direction of the accelerator pedal is effective only up to attainment of the neutral position of the accelerator pedal.
When besides the accelerator pedal a brake pedal is also provided, all of the embodiments of the apparatus according to the invention are preferably extended by a further device which, upon an actuation of the brake pedal, ensures that the braking-force generator generates braking force in accordance with said actuation. This means that the braking function of the accelerator pedal is deactivated when the driver actuates the brake pedal. It is thereby ensured that the driver, when he uses the brake pedal, may as usual proportion the braking force over the entire braking-force range.
By means of the previously described device or an additional device the apparatus according to the invention may also be developed in such a way that the braking function of the accelerator pedal is cut off when, for example, a vehicle dynamics control system of the vehicle comes into action. Although the device or devices in their simplest form of construction may be realized by a switch or a displacement potentiometer, in preferred embodiments a preferably electronic control unit is provided for realizing the more complex modes of behaviour. Said control unit may also communicate with sensors of other vehicle systems, e.g. with the sensors of a vehicle dynamics control system, and the signals of said sensors may be used to vary the predetermined braking force and to modify the function used to build up and/or reduce said braking force. The control unit may be a suitably modified, existing control unit of the brake system.
The initially stated object is achieved according to the invention also by a method of controlling the road speed of a motor vehicle, which comprises a brake system and an accelerator pedal, which is biased counter to its actuating direction into an inoperative position and through the actuation of which the instantaneous drive power of the motor vehicle drive may be varied, having the steps:
injecting a predetermined braking force into the brake system when the accelerator pedal is situated in its inoperative position,
automatically controlled reducing of the predetermined braking force injected into the brake system as soon as the accelerator pedal is moved from its inoperative position towards a neutral position, and automatically controlled building-up of the previously described braking force as soon as the accelerator pedal reattains its inoperative position, and
increasing the instantaneous drive power of the motor vehicle drive by moving the accelerator pedal beyond the neutral position.
According to an alternative, the initially stated object is achieved according to the invention also by a method of controlling the road speed of a motor vehicle, which comprises a brake system and an accelerator pedal, which is biased counter to its actuating direction into an inoperative position and through the actuation of which the instantaneous drive power of the motor vehicle drive may be varied, having the steps:
injecting a predetermined braking force into the brake system when the accelerator pedal is situated in its inoperative position,
moving the accelerator pedal from the inoperative position into a neutral position and reducing the predetermined braking force injected into the brake system in accordance with the movement of the accelerator pedal, such that in the neutral position no braking force or substantially no more braking force is injected into the brake system,
moving the accelerator pedal from the neutral position into the inoperative position and increasing the braking force injected into the brake system in accordance with the movement of the accelerator pedal up to the predetermined braking force, and
increasing the instantaneous drive power of the motor vehicle drive by moving the accelerator pedal beyond the neutral position.
As already described in connection with the apparatus according to the invention, in the method according to the invention also the predetermined braking force is varied preferably in dependence upon the road speed and/or driving style and/or road inclination and/or speed of easing off the accelerator pedal and/or further parameters.